Since no one from that site has explained exactly what the problem is, I can only make an educated guess:
Mp3sale uses multiple servers for storage, the newer server(s) seem to be where the problem exists. When they say newer releases don't download, what they must mean is "new" to be located and reside on that new server. I have a CD from 1997 & 2004 that won't download, so year of release isn't totally relevant, although one would surmise that the newer stuff is being put on newer servers (the ones with the problems). The mp3's that successfully download are more than likely on a different, unaffected bank of servers. So basically it's a crapshoot depending on where the target download resides.
I could be off on this diagnosis, but hey...it's better than no info whatsoever.
Hopefully, pastor39 can give an update at some point, rather than people guessing, etc.